The smooth shifting of a valve plunger from one position to another is an important factor in valve design. It is a known fact that it takes more power to move a valve plunger from a stationary position and the pressure so required is commonly termed the breakaway pressure. Valves heretofore made have required a high degree of breakaway pressure and this has pretty well ruled out the use of a reasonable sized solenoid for moving the valve plunger, and has dictated the need for fluid power and a fluid controlled valve to deliver the required force needed to shift the valve plunger.
My invention makes it possible to shift the valve plunger with a low breakaway pressure and this has permitted the use of an industry standardly-accepted solenoid for this purpose. In addition, because of the low breakaway pressure required, the plunger may have a spring return that is reliable at all times. An important factor of my invention is the combination of a low friction seal between the external surface of the valve plunger and the internal surface of the bore in which the plunger reciprocates, together with a small diameter plunger having a high degree of finish on its external surface, and a construction wherein fluid pressure is from the interior of the plunger when a plunger port crosses a seal.